This invention relates to headliners for vehicles such as trucks and automobiles.
Headliners are used in the passenger compartments of various types of vehicles. They provide an aesthetically pleasing appearance, acoustical and vibrational damping, and in some cases incorporate energy-absorbing components intended to reduce risk of injury in a collision or other accident. The headliner may also provide a certain amount of structural reinforcement to the vehicle. To achieve these things, the headliner in many cases includes a structural polymer foam component. Various types of headliner designs are described in U.S. Pat. Nos. 5,833,304, 6,204,209, 6,887,552 and 6,939,491, US Published Patent Applications No. 2004/0235376 and 2004/0235378, and WO publications 2001/54949, 2002/04252, 2002/42119 and 2004/80710.
WO 2002/04252 describes a headliner that includes a “urethane matrix”. The urethane matrix includes a layer of fiberglass impregnated with a polyurethane foam. This matrix is formed by spraying a foam-forming composition onto the fiberglass layer. Additional layers are applied to each side of the urethane matrix, and the entire assembly is then placed into a heated mold, in which the foam-forming composition cures and the various layers become adhered together.
The manufacturing process described in WO 2002/04252 can yield good quality headliners, but manufacturing costs are higher than desired. Production rates are a primary cause of the excessive costs. Two factors play a significant role in production rates. The first of these is the so-called “demold time”, which refers to the amount of time the polyurethane foam formulation must be cured in the mold in order to form a dimensionally stable part. Parts that are demolded too soon often exhibit post-demold expansion, and become distorted or do not fit properly with other components of the headliner or with other parts of the vehicle. Polyurethane foam formulations that have been used in this process generally require 90 seconds or more of residence time in the mold.
A second factor that significantly affects production rates is the length of time after demolding that the part must be aged before being assembled to other components. A downstream process of particular interest involves a thermal bonding lamination step, in which a show surface is bonded to the composite. The bonding layer is typically an adhesive film that is bonded to the surface of the part during the molding step. If the lamination step is performed too soon after demolding, the polyurethane foam tends to degas during the lamination step. This leads to bubble formation at the interface of the adhesive and the polyurethane foam, as well as distortion of the part. Therefore, it is commonly necessary to hold the molded parts for 2 hours or more before this lamination step is performed.
The long demold times limit the capacity of the equipment—therefore, fewer production lines would be needed if the demold time could be reduced. The long hold times mean that parts have to be stored and inventoried, and introduce complexities (with associated costs) to the sequencing of the molding step and subsequent lamination process.
For these reasons, it would be desirable to reduce the demold times and reduce the post-molding holding time that are required in this process. In so doing, it is necessary to maintain the other performance attributes of the headliner assembly, including its physical properties and integrity.